The 300 loader has more lift capacity at the maximum height then Rob's #70 or my 419 (which tells us something, doesn't it?). However, it's still only around 720 pounds or so.
When you investigate grapplers, the weight of the
grapple will have to be subtracted from your lifting capacity to see what you could handle. If the
grapple replaces the bucket, you'd subtract the bucket weight from the
grapple weight. The result would be subtracted from the maximum lifting capacity.
There are the multi-tine (I don't know if "tine" is the correct term) grapples and there is a single tine
grapple, which may be your best option.
There's also a single tine
grapple that fits to the bucket. That may have been a TBNer's own design, though.
I did a search on Goggle ("Loader Grapples"). There are many manufacturers. The cheapest I saw was about $2000 and did include the hydraulics.
If you find one for your tractor, it'll probably do well with brush. If you need to move logs, you probably need a bigger tractor then the 790.
Now, a question for Rob...can't you install a thumb on your backhoe, Rob? I wonder how well that would work as a
grapple?